1. Field of the Invention
The present invention relates to a slip control in a traction control system for a vehicle which reduces the torque of the drive wheels of a vehicle when an undue slip rate is produced in the drive wheels so that the drive torque is transmitted with high efficiency.
2. Description of the Prior Art
In recent years, there has been proposed a traction control system which reduces the drive torque transmitted to the drive wheels for preventing the acceleration property from being deteriorated when the drive wheels are in a substantial slip condition.
In Japanese Patent Public disclosure (JP A) No. 62-49545, laid open to the public in 1987, the slip control system judges whether or not the slip rate of drive wheels against the load surface is greater than a predetermined value. If the slip rate is smaller than the predetermined value, the slip control system reduces the engine output to eliminate the slip condition. When the slip rate is greater than the predetermined value, the slip control system adjusts the brake force acting on the drive wheels in order to suppress an excessive drive force to the drive wheels to thereby eliminate the slip condition.
According to the above slip control system, it is advantageous that when the vehicle is in a slip condition where the slip level of the drive wheels is relatively low or small, the slip condition is dealt with merely through engine output control. Thus, the burden of the brake system of the vehicle can be eased It should, however, be noted that the slip control makes the driver feel an under-power of the engine output.